Kidshealth.org is kind of like a better, more accurate version of about.com for themes related to growing up. There are three sections to the site: the parents section, the kids section and the teens section. While many of the same topics are covered across the three sections, each takes a different approach as to how the material is covered (writing style, graphics, vocabulary, etc.) and how much is covered.
I use kidshealth in a couple of ways. One, it's a great, simple reference tool for parents who are just starting to learn about good nutritional habits, aspects of their children's development, facts about disabilities, etc. Two, it gives me good insight into how I can explain complex topics to children. For example, for a workshop for siblings of children with disabilities, I might see how Kidshealth approaches explaining what mental $#*!ation, Down Syndrome, autism, etc. It's really a comprehensive website, and one of the first I go to when I need to explain something to parents or students (and it comes in Spanish translations, so I'd give it double hearts, if I could).